1. Field of the Invention
This invention relates to a heat pump system usable as an air-conditioning apparatus, a refrigeration apparatus, or a temperature-conditioning apparatus, and in particular, to such an apparatus provided with a refrigerant flow control system which allows for stable heat pumping operation by compensating for pressure decrease in the high pressure refrigerant line due to, for example, head difference and pressure loss in piping between the compressor and the expansion valve, accompanied by pressure loss due to excessive radiation heat in the piping.
2. Background of the Art
A heat pump system, which is used as an air-conditioning apparatus or a refrigeration apparatus, enables cooling or heating the air in a room or a refrigerator by circulating refrigerant in a refrigerant circulation line through an outside heat-exchanger (condenser), an expansion valve, an inside heat-exchanger (evaporator), and an accumulator in sequence, with a compressor driven by an engine or an electric motor, for example.
When an outside unit including an outside-heat exchanger (condenser) and a compressor is placed on the ground while an inside unit including an inside heat-exchanger (evaporator) is placed on a higher level such as on the third or fourth floor, and an expansion valve is also located on a higher level, pressure loss in piping increases. Pressure loss in piping can occur for various reasons, e.g., flow resistance and a pressure decrease due to excessive radiation heat. In such cases, cooling or heating operation is conducted with significant pressure loss.
In addition, in a freezing system, when an outside unit including a condenser (an outside heat-exchanger) and a compressor is placed on the ground while an inside unit including an inside heat-exchanger (evaporator) is placed on a higher level such as on the second or third floor, and an expansion valve is also located on a higher level, pressure loss in piping increases. Pressure loss in piping can occur for other reasons, e.g., due to excessive radiation heat in piping. In such cases, freezing operation is conducted with significant pressure loss.
As understood from the above, when a heat pump system is operated as an air-conditioning apparatus to cool or heat the air in a room or as a refrigeration apparatus to cool the air in a storage compartment of a refrigeration apparatus, wherein there is a great head difference between the compressor and the expansion valve, the pressure in the high pressure refrigerant line in the vicinity of and upstream of the expansion valve decreases. Also, when the length of pipes used in the high pressure refrigerant line from the compressor to the expansion valve in these systems is long, the pressure in the high pressure refrigerant line in the vicinity of and upstream of the expansion valve decreases. Further, when the refrigerant loses too much heat, radiation heat, in the lengthy piping on the high pressure side, the pressure in the vicinity of and upstream of the expansion valve also decreases. In addition, when the length of pipes used in the low pressure refrigerant line from the expansion valve to the compressor in these systems is long, the intake pressure of the compressor decreases. When the intake pressure decreases, the discharge pressure also decreases, and the volume of the discharge refrigerant decreases. The volume of the refrigerant passing through the condenser decreases, and thus, the radiation area per refrigerant weight/time increases, i.e., more liquid refrigerant condenses, thereby reducing the pressure upstream of the expansion valve. Thus, the discharge pressure decrease in addition to the pressure decrease due to the increased condensation efficiency leads to a decrease in the pressure in the high pressure refrigerant line in the vicinity of and upstream of the expansion valve.
As described above, when the pressure in the high pressure refrigerant in the vicinity of and upstream of the expansion valve decreases, the difference between the high pressure upstream of the expansion valve and the low pressure downstream of the expansion valve becomes small, resulting in decrease in the amount of the refrigerant passing through the expansion valve. As a result, the cooling, heating, or freezing capacity is reduced.